Process for making pen/pet blends and transparent articles therefrom

ABSTRACT

Process for controlling the change of intrinsic viscosity and transesterification during solid stating of a polyethylene terephthalate (PET) and polyethylene naphthalate (PEN) blend, with an effective amount of an ethylene glycol compound. The process enables the production of a copolymer based on predefined initial and final IV&#39;s and final transesterification level, by varying the solid-stating time and/or effective amount of ethylene glycol. In one embodiment, a relatively greater amount of post-consumer PET (e.g., 70%) having an IV of on the order of 0.72-0.73, is incorporated in the blend to provide a final IV on the order of 0.80-0.85, and a moderate, controlled level of transesterification; the blend is used to injection mold a sleeve layer of a preform. In another embodiment, a substantially transparent neck finish for a preform is made from a PEN/PET blend having an amount of ethylene glycol which enables substantial transesterification, without excessive increase in IV.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This is a continuation application of U.S. Application Ser. No.09/308,787 filed Jul. 23, 1999 which is a continuation under 35 U.S.C.§371 of PCT Application US97/22353 filed Dec. 5, 1997, which claimspriority to U.S. application Ser. No. 08/760,918 filed Dec. 6, 1996 nowissued as U.S. Pat. No. 5,902,539.

FIELD OF THE INVENTION

[0002] The present invention concerns a process for making polyethylenenaphthalate and polyethylene terephthalate blends, and more particularlyto a method of controlling the change of intrinsic viscosity and levelof transesterification during solid stating of such blends.

BACKGROUND OF THE INVENTION

[0003] Polyethylene naphthalate (PEN) has a significantly higher glasstransition temperature (T_(g)) than polyethylene terephthalate (PET),i.e., about 120° C. compared to 80° C., as well as a five timeimprovement in oxygen barrier property. PEN is thus a desirable polymerfor use in thermal-resistant beverage containers (e.g., hot-fillable,refillable and/or pasteurizable containers), and for packagingoxygen-sensitive products (e.g., beer, juice). However, PEN is moreexpensive (both as a material and in processing costs) than PET and,therefore, the improvement in properties must be balanced against theincreased expense.

[0004] One method of achieving an article that is lower in cost thanPEN, but with higher thermal and barrier properties, is to provide ablend of PEN and PET. However, blending of these two polymers oftenresults in an opaque material with incompatible phases. Efforts toproduce a clear container or film from a PEN/PET blend have been ongoingfor over ten years, but there is still no commercial process inwidespread use for producing such articles.

[0005] One suggested method for making substantially transparent PEN/PETblends is a solid-stating process which increases the level oftransesterification (copolymerization) between the two polymers. Forexample, WO 92/02584 (Eastman) states that transesterification occurswhen the melt blended, crystallized polymer is held at a temperaturebelow the melting point and subjected to an inert gas flow in order toraise the inherent viscosity and/or remove acetaldehyde. Thistransesterification is in addition to that occurring during meltblending and molding operations. However, Eastman reports that when thelevel of transesterification between the two polymers is very high, thecrystallinity and resultant physical properties of the blend are reducedto the point where they are undesirable for making oriented containerswith good mechanical properties.

[0006] Eastman teaches the addition of a phosphorus stabilizer forcontrolling (reducing) the amount of transesterification which occursduring solid stating. In this way, Eastman claims to limit the amount oftransesterification to an amount no greater than about 20%, based on atheoretical maximum amount of transesterification being equal to 100%.For example, in Table 2 Eastman describes the transesterification andinherent viscosity of various solid-stated PEN/PET blends, where theinitial inherent viscosity of the blend was on the order of 0.55 to0.65, and the final inherent viscosity was about 0.80 to 0.85. In acontrol example (50-50 PEN/PET) the final inherent viscosity wasacceptable (0.86) after eight hours, but the percent transesterification(25.0) was too high (above 20%). By adding 0.5 or 1.0% Ultranox 626 (aphosphite stabilizer) in the first two examples, the Eastman processprovided a final inherent viscosity of 0.80 to 0.84 after eight hours,and an acceptable percent transesterification of 17.0 or 19.0 (below20%). The other three stabilizers/metal deactivators tested in Table 2failed to provide the final desired inherent viscosity andtransesterification levels.

[0007] Although the Eastman process may be suitable for certain limitedstarting materials and desired transesterification levels, it cannot beexpanded generally to different combinations of intrinsic viscosity,solid-stating time, and levels of transesterification. For example, ofpotential interest is a blend made from precursor homopolymer PEN andpost-consumer PET (PC-PET). The intrinsic viscosity of PC-PET is muchhigher than that of virgin fibre-grade PET, so that a blend ofPEN/PC-PET would require a relatively larger amount oftransesterification per unit intrinsic viscosity increase (compared to ablend of PEN/virgin PET). Hence, among other disadvantages, the priorart does not provide a process that allows a desired level of bothintrinsic viscosity and transesterification level.

[0008] It is possible to make substantially transparent preforms (forblow molding into containers) with a PET/PEN blend, without solidstating, but the disadvantages are such that the process is notcommercially viable. First, the preform injection molding temperature(i.e., barrel temperature) and/or the equilibration time (i.e., time inthe barrel) must be increased such that the resulting process is notcost-efficient or sufficiently reproducible for a commercial process.For example, in certain cases, the barrel time would be increased by afactor of four (i.e., an increase over the standard cycle of 45 secondsof up to 180 seconds); as a result, one would probably not be able torun the process on a standard injection molding machine. Furthermore,the increase in barrel time/temperature increases the acetaldehyde (AA)levels in the preform to an unacceptably high level, such that AA islikely to be extracted into the food product and produce an off taste,particularly with a product such as bottled water. Thus, this has notproven to be the desired solution.

SUMMARY OF THE INVENTION

[0009] According to the present invention, a process is provided forcontrolling both the rate of change of intrinsic viscosity (IV) and therate of transesterification of a blend of polyethylene terephthalate(PET) and polyethylene naphthalate (PEN) during solid stating. Themethod comprises providing PEN having a first intrinsic viscosity (IV),providing PET having a second IV, and reacting the PEN and PET in thepresence of an ethylene glycol compound in an amount sufficient toachieve a desired final IV and final level of transesterification in thecopolymerized PEN/PET product.

[0010] In one embodiment, a full-length preform sleeve layer is madefrom a PEN/PET blend having an effective amount of ethylene glycol toincrease the T_(g) at least about 15° C. Other layers of the preformbody may be PET. In this embodiment, a moderate, controlled level oftransesterification is provided to enable strainorientation/crystallization in both the blend and PET layers foroptimizing the mechanical performance, while maintaining optical clarity(substantial transparency).

[0011] In another embodiment, the process is used for making containerpreforms having a neck finish with a transesterification level of atleast about 30% or greater. For example, a 30% PEN and 70% PET weightpercent blend includes an effective amount of ethylene glycol to obtaina desired high level of transesterification, but without raising themolecular weight (i.e., intrinsic viscosity) too high. This blend willprovide a high T_(g) neck finish portion and is also melt compatiblewith adjacent PET layers to maintain clarity and adhesion. Because theneck finish is not stretched, there is no need to provide a lower levelof transesterification as would be required to enable strainorientation/crystallization.

[0012] In other embodiments, the method of this invention enables theuse of initial higher molecular weight polymers. For example, it may bedesirable to utilize post-consumer PET (PC-PET), having an initial IV of0.72-0.73 dL/g, in an amount of from about 60-90 weight percent, withthe remaining component being PEN. A predetermined final IV andtransesterification level are achieved by adjusting the solid statingtime and/or amount of ethylene glycol used.

[0013] The alkylene glycol preferably has up to 6 carbon atoms, morepreferably 2 or 3 (propylene or ethylene), and more preferably 2(ethylene). It may be precompounded with the PET and PEN, or added tothe reaction chamber in which the PET and PEN are copolymerized.Preferred amounts of the alkylene glycol include at least 0.05 weightpercent based on the total weight of PET and PEN, more preferably 0.1 to2 weight percent, and most preferably 0.1 to 0.5 weight percent.

[0014] These and other features and advantages of the present inventionare more particularly described with regard to the following detaileddescription and drawings.

BRIEF DESCRIPTION OF THE FIGURES

[0015] FIGS. 1-2 are graphs showing the change in melting temperature(MP) and orientation temperature (T_(g)) for various PEN/PET randomcopolymer compositions;

[0016]FIG. 3 is a cross-sectional view of a preform embodiment of thepresent invention having a full-length inner body sleeve of the PEN/PETblend;

[0017]FIG. 4A is a front elevational view of a returnable and refillablecarbonated beverage container, partially in section, made from thepreform of FIG. 3, and FIG. 4B is an enlarged fragmentary cross-sectionof the container sidewall taken along the line 4B-4B of FIG. 4A;

[0018]FIG. 5A is a cross-sectional view of another preform embodiment ofthe present invention having a monolayer neck finish insert and amultilayer body portion, and FIG. 5B is an enlarged fragementary crosssection view of the neck finish/body junction of the preform of FIG. 5A;

[0019]FIG. 6 is a graph of intrinsic viscosity versus solid-stating timeillustrating the rate of IV increase for various compositions;

[0020]FIG. 7 is a graph of the percent transesterification versussolid-stating time illustrating the rate of transesterification forvarious compositions;

[0021]FIG. 8 is a graph of the initial drop in intrinsic viscosity as afunction of the weight percentage of ethylene glycol added to thereaction mixture prior to solid stating;

[0022]FIG. 9 is a graph of the rate of intrinsic viscosity gain versusthe weight percentage of ethylene glycol added to the reaction mixtureprior to solid stating; and

[0023]FIG. 10 is a graph of the rate of transesterification as afunction of the weight percentage of ethylene glycol added to thereaction mixture prior to solid stating.

DETAILED DESCRIPTION

[0024] When PET/PEN blends are subjected to a solid-stating process, forexample to increase the IV and/or to reduce acetaldehyde generation, theamount or level of transesterification is increased, based on atheoretical maximum amount of transesterification (randomcopolymerization) of 100%. Transesterification is measured by nuclearmagnetic resonance spectroscopy (NMR)—more specifically by determiningthe relative area in the NMR curves of the ethylene protons associatedwith naphthalene-dicarboxylate-ethylene glycol-terephthalate units,compared to what would be found for a completely random copolymer madewith naphthalenedicarboxylic acid, terephthalic acid, and ethyleneglycol. The random copolymer would be considered to have 100%transesterification. See WO92/02584 (Eastman).

[0025] The PEN/PET blend may be formed by extrusion compounding,pelletizing, crystallizing and then solid stating to a desiredtransesterification level. Subsequently, it is contemplated that thesolid-stated polymer will be extruded or injection molded to form apreform; this step is likely to produce a reduction in IV and increasein transesterification. Finally, the preform will be expanded (e.g.,blow molded) into a substantially transparent container or otherarticle.

[0026] There are three significant variables in the solid-statingprocess, namely the change in IV, the solid-stating time, and the changein transesterification level. Temperature is also important but isusually set to the highest temperature possible without melting thepolymer blend. Generally, for a given application, the initial and finalIV are specified, as well as the final level of transesterification. Itwould be desirable to control the process to achieve these predeterminedparameters, by adjusting the solid-stating time and/or by the use ofadditives. According to the present invention, the amount of ethyleneglycol present during the solid-stating process can be used to controlboth the rate of change of IV and the rate of transesterification. Inparticular, it has been found that adding an increasing amount ofethylene glycol to the blend prior to solid stating results in acopolymer having a higher level of transesterification. This result issurprising since conventional wisdom indicates that adding ethyleneglycol to the reaction mixture would result in a decrease in the levelof transesterification of the resulting copolymer.

[0027] More particularly, it is desirable to add PEN to a PET polymer inorder to increase the thermal performance, i.e., T_(g). However, at PENlevels on the order of 20-80 weight percent in a random copolymer (seeFIGS. 1-2), the blend is substantially amorphous, which means thematerial cannot be crystallized. Generally, a crystallizable material isrequired in a stretch blow-molded article because it provides thenecessary levels of orientation and barrier properties, and controls thematerial distribution. Also, with PET/PEN blends, there is a problemwith incompatible phases rendering the article opaque.

[0028] Generally, too low a level of transesterification provides aPEN/PET preform of poor clarity (i.e., not substantially transparent),while too high a level of transesterification prevents crystallinity(i.e., strain-induced crystallization and the resulting improvedmechanical properties). Thus, in certain applications there is someintermediate level of transesterification desired in order to obtainboth substantial transparency and good mechanical properties. Thespecific level of transesterification required will vary with therelative amounts of the polymers, their IV's, layer thicknesses, usetemperature, use of copolymers, etc.

[0029] In other applications, the PEN/PET blend may have a relativelyhigh level of transesterification. The copolymers of the presentinvention having a transesterification of greater than about 30%demonstrate properties similar to copolymers having atransesterification level of about 100% (i.e., truly random copolymers).Thus, a relatively high level of transesterification as used hereinrefers to a copolymer having a transesterification level of greater thanabout 30%, and more preferably greater than about 35%. As known to thoseskilled in the art, the actual level of transesterification at which acopolymer demonstrates the properties of a truly random copolymerdepends on a variety of parameters.

[0030] FIGS. 1-2 illustrate graphically the change in melt temperature(MP) and orientation temperature (T_(g)) for PET/PEN near randomcopolymer compositions, as the weight percent of PEN increases from 0 to100. There are three classes of PET/PEN compositions: (a) a high-PENconcentration having on the order of 80-100% PEN and 0-20% PET by totalweight of the composition, which is a strain-hardenable (orientable) andcrystallizable material; (b) a mid-PEN concentration having on the orderof 20-80% PEN and 80-20% PET, which is an amorphous non-crystallizablematerial that, when at a relatively high level of transesterification,will not undergo strain hardening; and (c) a low-PEN concentrationhaving on the order of 1-20% PEN and 80-99% PET, which is acrystallizable and strain-hardenable material. A particular PEN/PETcomposition can be selected from FIGS. 1-2 based on the particularapplication.

[0031] The PEN and PET polymers useful in the blends of this inventionare readily prepared using typical polyester polycondensation reactionconditions known in the art. They can be made by either a batch orcontinuous process to a desired IV value. Examples of methods which maybe employed to prepare the PET and PEN polymers useful in the presentinvention are found in U.S. Pat. No. 4,617,373.

[0032] For example, polyethylene naphthalate (PEN) is a polyesterproduced when dimethyl 2,6-naphthalene dicarboxylate (NDC) is reactedwith ethylene glycol. The PEN polymer comprises repeating units ofethylene 2,6 naphthalate. PEN resin is available having an inherentviscosity of 0.67 dl/g and a molecular weight of about 20,000 fromEastman Chemical Co., Kingsport, Tenn. PEN has a glass transitiontemperature T_(g) of about 123° C., and a melting temperature MP ofabout 267° C.

[0033] Either or both of the PET and PEN polymers may optionally bemodified with various materials such as dicarboxylic acids, glycols,cyclohexanes, xylenes and bases appropriate for amide formation. Suchmodifying materials are typically precompounded with the PET or PEN.Thus, as used herein PET and PEN are meant to include such modifiedpolymers.

[0034] When dicarboxylic acids are used as the modifying materials, thePEN or PET should include up to 15 mol %, and preferably up to 10 mol %,of one or more of the dicarboxylic acids (i.e., different thannaphthalenedicarboxylic acid isomer(s) in the case of PEN and differentthan terephthalic acid isomer(s) in the case of PET) containing 2 to 36carbon atoms, and/or one or more different glycols (i.e., different thanethylene glycol) containing 2 to 12 carbon atoms.

[0035] Typical modifying dicarboxylic acids for PEN includeterephthalic, isophthalic, adipic, glutaric, azelaic, sebacic, fumaricand stilbenedicarboxylic acid and the like. Typical examples of amodifying glycol for PEN include 1,4-butanediol, 1,6-hexanediol,2,2-dimethyl-1,3-propanediol, 1,4-cyclohexanedimethanol, and the like.The PEN polymers are preferably derived from 2,6-naphthalenedicarboxylicacid, but may be derived from 2,6-naphthalenedicarboxylic acid and alsocontain, optionally, up to about 25 mol % (preferably up to 15 mol %,more preferably up to 10 mol %) of one or more residues of differentnaphthalenedicarboxylic acid isomers such as the 1,2-, 1,3-, 1,4-, 1,5-,1,6-, 1,7-, 1,8-, 2,3-, 2,4-, 2,5-, 2,7- or 2,8-isomers. PEN polymersbased primarily on 1,4-, 1,5-, or 2,7-naphthalenedicarboxylic acid arealso useful.

[0036] Typical glycols used for modifying PEN include but are notlimited to alkylene glycols, such as ethylene glycol, propylene glycol,butylene glycol, pentylene glycol, 1,6-hexanediol, and2,2-dimethyl-1,3-propanediol.

[0037] Cyclohexane modifiers appropriate for use with PEN arenonaromatic 6-member ring compounds which can act as base portions incondensation reactions. Such compounds include, for example,1,4-cyclohexane dimethanol (CAS #105-08-8, available from AldrichChemicals, Milwaukee, Wis., USA). Xylenes appropriate for modifying PENare benzene-containing compounds which include at least one methyl groupbonded to the benzene ring and which may have additional alkyl groupsbonded to the benzene ring. Such xylenes include, for example, toluene,xylene, methylethylbenzene, methylpropylbenzene and methylbutylbenzene.

[0038] PEN modifying amide-forming bases appropriate for use in thepresent invention include metaxylenediamine (CAS #1477-055-0, availablefrom Aldrich Chemicals), hexamethylenediamine (CAS #124-09-4, availablefrom Aldrich Chemicals), and the like.

[0039] Typical modifying dicarboxylic acids for PET include isophthalicacid, adipic acid, glutaric acid, azelaic acid, sebacic acid, fumaricacid, stilbenedicarboxylic acid, biphenyldicarboxylic acid, any of theisomers of naphthalenedicarboxylic acid, and the like. Typical modifyingglycols for PET include alkylene glycols, such as ethylene glycol,propylene glycol, butylene glycol, pentylene glycol, 1,6-hexanediol,2,2-dimethyl-1,3-propanediol, and the like. The aforementionedcyclohexanes, xylenes and amides may also be used to modify PET.

[0040] Commercially available “bottle grade” PET includes PEThomopolymer and PET copolymers suitable for making containers, which arewell-known in the art. These PET copolymers may include a minorproportion, for example up to about 10% by weight, of monomer unitswhich are compatible with the ethylene terephthalate units. For example,the glycol moiety may be replaced by an aliphatic or alicylic glycolsuch as cyclohexane dimethanol (CHDM). The dicarboxylic acid moiety maybe substituted by an aromatic dicarboxylic acid such as isophthalic acid(IPA).

[0041] Post-consumer PET (PC-PET) is a type of recycled PET preparedfrom PET plastic containers and other recyclables that are returned byconsumers for a recycling operation, and has now been approved by theFDA for use in certain food containers. PC-PET is known to have acertain level of I.V. (intrinsic viscosity), moisture content, andcontaminants. For example, typical PC-PET (having a flake size ofone-half inch maximum), has an I.V. average of about 0.073 dl/g to about0.74 dl/g, a moisture content of less than 0.25%, and the followinglevels of contaminants:

[0042] PVC: <100 ppm

[0043] aluminum: <50 ppm

[0044] olefin polymers (HDPE, LDPE, PP): <500 ppm

[0045] paper and labels: <250 ppm

[0046] colored PET: <2000 ppm

[0047] other contaminants: <500 ppm

[0048] PC-PET may be used alone or in one or more layers for reducingthe cost or for other benefits.

[0049] The amount of PET in the blend (i.e., component (A)) ispreferably of from about 50 to about 90 weight %, and more preferably offrom about 60 to about 80 weight %. Accordingly, the amount of PEN inthe blend (i.e., component (B)) is preferably of from about 10 to about50 weight %, and more preferably of from about 20 to about 40 weight Anamount of ethylene glycol may be used effective to substantially reducethe rate of increase of intrinsic viscosity (molecular weight) duringsolid stating. The desired overall increase (or decrease) of IV andincrease in transesterification can be selected by varying the amount ofglycol weight percent, depending upon the particular initial and finalIV, transesterification level, and solid-stating time. Typically, theeffective amount of ethylene glycol would be at least about 0.05 weightpercent, based on the weight of the polymer blend, preferably from about0.1 to 2%, and more preferably from about 0.1% to 0.5%.

[0050] Suitable alkylene glycols have from 2 to 6 carbon atoms; i.e.,ethyl C₂, propyl C₃, butyl C₄, pentyl C₅, or hexyl C₆. Preferred glycolsare ethylene glycol (CH₂OHCH₂OH) and propylene glycol (CH₃CHOHCH₂OH).Particularly preferred is ethylene glycol, CH₂OHCH₂OH, a clear,colorless liquid having a specific gravity of 1.1155 (20° C.) and aboiling point of 197.2° C.

[0051] The solid-stating procedure which results in transesterificationof the PET/PEN blends can be any solid-stating procedure commonly usedin the polyester art to increase IV and/or reduce the acetaldehydeconcentration. Basically, solid stating is a procedure wherein a solidpolymer is heated until the desired level of IV build-up is achieved anda means for removing glycol during heating is provided. However,according to the present invention, the amount of ethylene glycolpresent is manipulated such that the desired final IV andtransesterification level are achieved.

[0052] The amount of heating is between the highest glass transitiontemperature (T_(g)) of the polymers present and the lowest meltingtemperature (MP) of the polymers present. Typically, the temperatureduring solid stating is between about 150° C. and about 250° C.,preferably between about 210° C. and 250° C., and more preferablybetween about 215° C. and about 230° C. The amount of IV build-up fortypical solid-stating process is an increase of at least about 5%, andpreferably at least about 10%. Usually, no more than a 50% increase inIV is desired, although higher build-up is commercially useful for someapplications (e.g., tire cord).

[0053] The time required for solid stating will vary; at least about 6hours, and up to about 30 hours, is typical. Preferably, no more thanabout 24 hours is desired.

[0054] Nitrogen flow or vacuum used during the solid-stating processmust be strong enough to remove ethylene glycol from the reactionmixture such that the amount of ethylene glycol present in the reactionmixture results in the desired final IV and transesterification level.There are two sources of this ethylene glycol. The first source is theethylene glycol that is added to the reaction mixture prior to thereaction, and the second source is the ethylene glycol formed as aby-product of the condensation reaction of functional end groups of thepolymer chains. It has been found that by adding a specified amount ofliquid ethylene glycol prior to the solid stating process, while drawingoff ethylene glycol during the reaction, that the IV andtransesterification rates can be controlled.

[0055] As is readily apparent to a skilled artisan, all parameters forsolid stating (such as time, temperature and chemical nature ofpolymer(s)) are interdependent and will be varied to accommodate aparticular desired result.

[0056] The compositions of the present invention are suited forhigh-temperature packaging applications such as hot-fillable, returnableand refillable, and pasteurizable food and beverage containers. Theparticular overall blend composition desired can be determined by thebarrier and thermal properties needed for the end use requirements.

[0057] The intrinsic viscosity (IV) affects the processability of thepolyester resin. Polyethylene terephthalate having an intrinsicviscosity of about 0.8 is widely used in the carbonated soft drinkindustry. Resins for various applications may range from about 0.6 toabout 1.2, and more particularly from about 0.65 to about 0.85. 0.6corresponds approximately to a viscosity average molecular weight of59,000, and 1.2 to a viscosity average molecular weight of 112,000.

[0058] Intrinsic viscosity measurements may be made according to theprocedure of ASTM D-2857, by employing 0.0050±0.0002 g/ml of the polymerin a solvent comprising o-chlorophenol (melting point 0° C.),respectively, 30° C. Intrinsic viscosity is given by the followingformula:

IV=(ln(v _(Soln.) /V _(Sol.)))/C

[0059] where:

[0060] V_(Soln.) is the viscosity of the solution in any units;

[0061] V_(Sol.) is the viscosity of the solvent in the same units; and

[0062] C is the concentration in grams of polymer per 100 mls ofsolution.

[0063] The I.V.s of PEN and PET polymers before solid stating aretypically about 0.5 to about 0.8, and more typically about 0.6 to about0.7. The IV's of the polymers after solid stating are typically about0.5 to about 1.0, and more typically about 0.7 to about 0.8.

[0064] The preform and blown containers should be substantiallytransparent. A measure of transparency is the percent haze fortransmitted light through the wall (H_(T)) which is given by thefollowing formula:

[0065]  H _(T) =[Y _(d), (Y _(d) +Y _(s))]×100

[0066]

[0067] where Y_(d) is the diffuse light transmitted by the specimen, andY_(S) is the specular light transmitted by the specimen. The diffuse andspecular light transmission values are measured in accordance with ASTMmethod D1003, using any standard color difference meter such as modelD25D3P manufactured by Hunterlab, Inc. A substantially transparentcontainer should have a percent haze (through the wall) of less thanabout 15%, preferably less than about 10%, and more preferably less thanabout 5%. A substantially amorphous preform should have a percent hazeof no more than about 20%, preferably no more than about 10%, and morepreferably no more than about 5%. The preform may be single layer ormultilayer and may be made in accordance with the well-known injectionmold processes, such as described in U.S. Pat. No. 4,710,118 grantedDec. 1, 1987 to Krishnakumar et al., which is hereby incorporated byreference in its entirety.

[0068] The materials, wall thicknesses, preform and bottle contours, mayall be varied for a specific end product while still incorporating thesubstance of this invention. The container may be for pressurized orunpressurized beverages, including beer, juice and milk, or fornon-beverage products.

[0069] The improved thermal resistance provided by this invention makesit particularly suitable for hot-fill containers. Hot-fill containerstypically must withstand elevated temperatures on the order of 180-185°F. (the product filling temperature) and positive internal pressures onthe order of 2-5 psi (the filling line pressure) without substantialdeformation, i.e., a volume change of no greater than about ±1%. Otherfactors important in the manufacture of hot-fill containers aredescribed in U.S. Pat. No. 4,863,046 to Collette et al. granted Sep. 5,1989, which is hereby incorporated by reference in its entirety.

[0070] The enhanced thermal resistance of the PEN/PET blends of thisinvention are also particularly useful as one or more layers of arefillable carbonated beverage container able to withstand numerousrefill cycles while maintaining aesthetic and functional features. Atest procedure for simulating such a cycle without crack failure andwith a ±1.5% maximum volume change is as follows.

[0071] Each container is subjected to a typical commercial caustic washsolution prepared with 3.5% sodium hydroxide by weight and tap water.The wash solution is maintained at the desired wash temperature, e.g.,60° C., 65° C., etc. The bottles are submerged uncapped in the wash for15 minutes to simulate the time/temperature conditions of a commercialbottle wash system. After removal from the wash solution, the bottlesare rinsed in tap water and then filled with a carbonated water solutionat 4.0±0.2 atmospheres (to simulate the pressure of a carbonated softdrink container), capped and placed in a 38° C. convection oven at 50%relative humidity for 24 hours. This elevated oven temperature isselected to simulate longer commercial storage periods at lower ambienttemperatures. Upon removal from the oven, the containers are emptied andagain subjected to the same refill cycle, until failure.

[0072] A failure is defined as any crack propagating through the bottlewall which results in leakage and pressure loss. The volume change isdetermined by comparing the volume of liquid the container will hold atroom temperature, both before and after each refill cycle.

[0073] The container can preferably withstand at least 10 refill cycles,and preferably 20 refill cycles at a wash temperature of at least 60° C.without failure, and with no more than about ±1.5% volume change intotal.

[0074] For use as a refillable bottle, the bottle preferably has arelatively thick champagne base made in accordance with the prior artrefill containers described in Continental PET Technologies, Inc.'s U.S.Pat. Nos. 4,725,464 and 5,066,528, which are hereby incorporated byreference in their entirety. The dome and chime form a thickened baseportion having about 3-4 times the thickness of the cylindricalsidewall, and having an average crystallinity of no greater than about10%. Radially outwardly of the chime, there is a thinner outer baseportion of about 50-70% of the thickness of the thickened base portionand increasing in crystallinity up to its junction with the sidewall.The thinner outer base wall provides improved impact resistance. Thethickened dome and chime provide improved resistance to causticcracking.

[0075] A preferred planar stretch ratio is 8-12:1 for a cylindricalsidewall of a polyester refill beverage bottle of about 0.5 to 2.0liters/volume, and more preferably about 9-11:1. The hoop stretch ispreferably 3-3.6:1 and the axial stretch 2.4-3:0. This produces acontainer sidewall with the desired abuse resistance, and a preformsidewall with the desired visual transparency. The sidewall thicknessand stretch ratio selected depend on the dimensions of the specificbottle, the internal pressure (e.g., 2 atm for beer, 4 atm for softdrinks) and the processing characteristics of the particular material(as determined for example, by the intrinsic viscosity).

[0076] The cylindrical sidewall portion of the container which is blownto the greatest extent has the highest average percent crystallinity,preferably about 25-35%. The tapered shoulder, which is also expandedsubstantially more than the base, preferably has an average percentcrystallinity of 20-30%. In contrast, the substantially thickened andlesser blown base has a crystallinity of about 0-10% in the dome andchime, and increases in crystallinity in the outer base moving upwardlytowards the sidewall. The neck finish is not expanded and remainssubstantially amorphous at 0-2% crystallinity.

[0077] Various levels of crystallinity can be achieved by a combinationof expansion (strain-induced) and heat-setting (thermal-induced).

[0078] Methods of making a full-length sleeve and/or separate neckfinish portion according to the examples shown in FIGS. 3-6 aredescribed in copending and commonly owned U.S. Ser. No. 08/534,126 filedSep. 26, 1995, entitled “PREFORM AND CONTAINER WITH CRYSTALLIZED NECKFINISH AND METHOD OF MAKING THE SAME,” by Wayne N. Collette and SuppayanM. Krishnakumar, which in turn is a continuation-in-part of copendingand commonly owned U.S. Ser. No. 08/499,570 filed Jul. 7, 1995, entitled“APPARATUS AND METHOD FOR MAKING MULTILAYER PREFORMS,” by Suppayan M.Krishnakumar and Wayne N. Collette, both of which are herebyincorporated by reference in their entirety.

[0079]FIG. 3 shows a preform 30 which includes an outer layer 22 and afull-length inner sleeve layer 20, the sleeve having a portion 21extending over the top sealing surface of the neck finish.

[0080] FIGS. 4A-4B illustrate a refillable carbonated beveragecontainer, which has been stretch blow molded from the preform of FIG.3. The multilayer container 40 includes in cross-section abiaxially-expanded inner layer 41 formed from the preform inner sleevelayer 20, and biaxially-expanded outer layer 43 (formed from preformouter layer 22). The container includes an upper neck finish 42 (same asin the preform), a dome-shaped shoulder section 44, a cylindrical panelsection 45, and a base 48. The base includes a recessed central dome 52,surrounding a central gate 51, a standing ring or chime 54 surroundingthe dome, and an outermost base region 56 connecting the chime to thesidewall. FIG. 4B is an expanded view of the multilayer panel section45, showing a relatively thin inner layer 41 and relatively thickerouter layer 43. The PEN/PET blend of the present invention may be usedas either the inner or outer layers, with the other layer being PET oranother compatible polymer. As a cost savings to minimize the use ofPEN, the inner layer 41 may be the PEN/PET blend.

[0081] FIGS. 5A-5B illustrate another preform embodiment. In this case,a monolayer neck finish is made of the PEN/PET blend, to provide thermalresistance. This is particularly useful in hot-fillable containers. Amultilayer body portion may include one or more layers of PET, PC/PET, aPET/PEN blend of the present invention, or other compatible polymers.The container 330 includes a neck finish portion 340 and body portion350. The neck finish includes an open upper end 342 including a topsealing surface 341, external threads 343, and a lowermost flange 344.The body portion 350 includes an upper tapered portion 351, which willform the shoulder portion of the container, a cylindrical body portion352, which will form the panel of the container, and a lowerbase-forming portion 353. In this example, the body portion includesouter layer 354, core layer 356, and inner layer 358. In the centralbase portion there is a further layer 359 which is generally made toclear the nozzle of the core material, in preparation for the nextinjection molding cycle.

[0082] The following examples illustrate the invention, but should notbe interpreted as a limitation thereon.

EXAMPLE 1 PET/PEN

[0083] 33.7 lbs of clean post-consumer PET flake, with an average IV of0.74, and 16.3 lbs of pellets of a homopolymer PEN, with an IV of 0.67,are hand blended and dried at 300° F. using a D-100 desiccant dryer fromConair for a period of 8-10 hours at a dew point of −40° F. or lower.The 50-lb dried blend is then compounded on a 1½″ extruder with a 36:1L/D ratio and a compression ratio of 3:1. The entire transition zone isof a barrier design with a 0.010″ clearance between the screw andbarrel. The output of the extruder is directed into a stranding dye;molten strands are then pulled through a water bath for cooling, and arefinally chopped into ¼″ long by _″ diameter pellets with a final IV of0.68.

[0084] These pellets are then dried in vacuum with agitation at 250° F.for 3 hours; they are then crystallized under vacuum with agitation at350° F. for an additional hour before solid stating at 430° F. underhigh vacuum and agitation for a period of 24 hours in a Ross, HauppaugeN.Y., VB-001 Double Planetary Mixer. Processing of these materials underthese conditions yielded a transesterification level of 20%. The 24hours of solid stating at an IV rate increase of 0.012/hr yieldedpellets with an unacceptably high IV of 0.97. Although the 20%transesterification rate targeted in this example was achieved, and thetime of solid state processing was reasonable, the final IV was too highto be used for commercial production of stretch-blow molded bottles.

EXAMPLE 2 PET/PEN with 1% Ultranox 626

[0085] The same compounding steps as in Example 1 were conducted, but tothe 50-lb dried blend was added 1% (by weight) Ultranox 626 (Eastman'sphosphite stabilizer) and blended by hand. The pellet IV was 0.69. Thepellets were then dried, crystallized and solid stated as in Example 1,but the solid-stating time was 36 hours. The transesterification ratewas 0.29/hour, and final transesterification level 10.5%. The 36 hoursof solid stating at an IV rate increase of 0.021/hr, yielded pelletswith an unacceptably high IV of well over 1.1. Thus, not only was thetransesterification level below target, but the IV was too high toproduce bottles. Also, the 36 hours of processing time was somewhatexcessive and not generally suitable for a commercial process.

EXAMPLE 3 PET/PEN with 0.5% Ethylene Glycol

[0086] The same compounding steps as in Example 1 were conducted but tothe 50-lb dried blend was added 0.5% (by weight) liquid ethylene glycoland mixed by hand in a bucket. The pellet IV was 0.50.

[0087] The pellets were dried, crystallized and solid stated as inExample 1, but the solid-stating time was 11 hours. The finaltransesterification level was 20%. The 11 hours of solid stating at anIV rate increase of 0.0056/hr yielded pellets with an IV of 0.55.Although a targeted 20% transesterification level was achieved, and thesolid-stating time was acceptable, the resultant IV was too low to beused for commercial production of stretch-blow molded bottles.

EXAMPLE 4 PET/PEN with 0.13% Ethylene Glycol

[0088] The same compounding steps as in Example 1 were conducted but tothe 50-lb dried blend was added 0.13% (by weight) liquid ethyleneglycol. The pellet IV was 0.54.

[0089] The pellets were dried, crystallized and solid stated as inExample 1, but the solid stating time was 21 hours. The finaltransesterification level was 20%. The 21 hours of solid stating at anIV rate increase of 0.010/hr yielded pellets with an IV of 0.76. Atargeted 20% transesterification level was achieved, the 0.76 IV wasacceptable, and the solid-stating time was acceptable for commercialproduction of stretch-blow molded bottles. This example shows howadjusting the amount of ethylene glycol and solid-stating time providedthe desired final IV and transesterification level.

EXAMPLE 5 Preform with PEN/PET Neck Finish

[0090] A preform utilizing a PEN/PET blend for the neck finish as shownin FIGS. 5A-5B was produced as follows.

[0091] 35 pounds of virgin PET pellets, with an average IV of 0.80, and15 pounds of homopolymer PEN pellets, with an average IV of 0.60, werehand blended and dried as in Example 1. In a polyethylene bucket, 0.3%ethylene glycol was added to the blend by hand. The mixture wascompounded as in Example 1. The pellet IV was 0.59.

[0092] The pellets were dried, crystallized and solid stated as inExample 1, but the solid-stating time was 26 hours. The finaltransesterification level was 35%; the IV rate increase was 0.0082/hr toprovide a final IV of 0.80.

[0093] The state of the material as it came out of the reactor washighly crystalline, which allows for standard, PET drying and processingmethods to be used. However, when this material is later melted (duringinjection molding to form a preform), it does not recrystallize, but,rather, remains amorphous. The material's relatively high T_(g) of 92°C. allows it to withstand hot filling and pasteurizing temperatures whenincorporated into a preform neck finish. The comparatively hightransesterification level provides a material which is melt compatibleand generally adhering to adjacent layers of PET (i.e., resistingdelamination under normal use conditions).

[0094] The preform neck finish (as in FIG. 5A) may be produced on oneinjection molding machine, removed and placed within a second injectionmolding machine where the body portion is overmolded. Alternatively,both the body and the finish of the preform can be made by differentprocessing steps within the same injection molding machine. Therelatively high level of transesterification in the neck finish of thisexample is acceptable because it is not required to undergo strainoriented crystallization.

EXAMPLE 6 Gaseous Ethylene Glycol Added to Reactor

[0095] A theoretical example of a method of introducing ethylene glycolto control transesterification rate and IV increase rate is as follows.

[0096] 33.7 lbs. of clean post-consumer PET flake, with an average IV of0.74, and 16.3 lbs. of pellets of homopolymer PEN, with an IV of 0.67,are hand blended and dried at 300° F. using a D-100 desiccant dryer fromConair for a period of 8-10 hours at a dew point of −40° F. or lower.The 50-lb dried blend is then compounded on a 1½ extruder with a 36:1L/D ratio and a compression ratio of 3:1. The entire transition zone isof a barrier design with a 0.010″ clearance between the screw andbarrel. The output of the extruder is directed into a stranding dye;molten strands are pulled through a water bath for cooling, and arefinally chopped into ¼″ long by ⅛″ diameter pellets with a final IV of0.68.

[0097] These pellets are then dried in vacuum with agitation at 250° F.for 3 hours in a 1 cubic foot jacketed and agitated vacuum reactor; theyare then crystallized under vacuum with agitation at 350° F. for anadditional hour before raising the temperature to 430° F. and proceedingunder high vacuum (2 Torr) and agitation for a period of 2 hours. Theconnection from the reactor to the vacuum pump is then closed trappingthe vacuum within the reactor but stopping the removal of gases from it.400 grams of ethylene glycol is slowly added to the reactor maintainingtemperature and agitation for 4 hours. This is about double the amountof ethylene glycol added in the previous examples and it is expectedthat at least part of the ethylene glycol will diffuse into the pellets.The vacuum is then restored removing all remaining gaseous ethyleneglycol. The reaction is continued under vacuum for an additional 20hours. The pellets would be expected to have an IV of about 0.80 and atransesterification level of around 20%.

EXAMPLE 7 PET/PEN with Propylene Glycol

[0098] As a theoretical example, propylene glycol was substituted forethylene glycol in the above examples, using the same weight percent (asethylene glycol). It is expected that some amount of propyl groups willbe included in the copolymer backbone, and that the use of propyleneglycol instead of ethylene glycol (based on the same relative weightpercent) will provide a faster IV increase and slower rate oftransesterification.

[0099] FIGS. 6-11 and the following table illustrate the processingeffects caused by adding ethylene glycol to the solid stating processaccording to the present invention.

[0100] In the graph of FIG. 6, the Y axis is intrinsic viscosity (IV) asdetermined according to ASTM D/2857 (see prior discussion). On the Xaxis there is displayed the solid-stating time in hours, from 0 to 20hours. The compounding and solid-stating conditions were similar tothose described in the prior examples. As a reference (A)—see tablebelow—a composition of 100 weight % virgin PET 6307, available fromShell Company (Houston, Tex.), having an initial IV of 0.64 dL/g, wasused. After solid stating for about 16 hours, the final IV was 0.9, atan IV rate increase of 0.0163 (dL/g)/hour. As a control sample (B), acomposition of 8 molar % dimethyl terephthalate, and 92 weight %dimethyl-2,6-naphthalenedicarboxylate (PEN 15967 available from EastmanChemical Company, Kingsport, Tenn.), having an initial IV of 0.6338dL/g, was used. After about 14 hours of solid stating, the final IV was0.7641, at an IV rate increase of 0.012 (dL/g)/hour.

[0101] A first sample (C) according to the invention is the same as thecontrol sample but included in addition 0.125 weight % ethylene glycol.It had an initial IV of 0.5440; after about 17 hours of solid stating,the final IV was 0.7254 at an IV rate increase of 0.011/hour. A secondsample (D) according to the invention is the same as the control samplebut included in addition 0.5 weight % ethylene glycol. It had an initialIV of 0.4478; after about 16 hours of solid stating the final IV was0.5429 at an IV rate increase of 0.0056/hour. A third sample (E)according to the invention is the same as the control sample butincluded in addition 2 weight % ethylene glycol. It had an initial IV of0.3665; after about 15 hours of solid stating the final IV was 0.3151,at an IV rate decrease of −0.0036/hour. Note that the third sample (E)had an overall negative change (decrease) in IV, i.e., the polymerchains were breaking up at a faster rate than they were combining. Asindicated, each of the three samples (C, D, E) according to theinvention has a significantly lower IV rate increase than the controlsample (B).

[0102] As a further distinction, a sample (F) in accordance with theprior art Eastman patent included 67.4 weight % PET and 32.6 weight %PEN, and in addition 1 weight % of Ultranox 626 (the phosphatestabilizer); it had an initial IV of 0.6400 and a final IV of 0.9845after about 17 hours, for an IV increase rate of 0.021/hour. Again, thisis a significantly higher IV rate increase than the three samples (C, D,E) of the present invention.

[0103] The percent transesterification for the above copolymers B-F wasmeasured as a function of the amount of ethylene glycol for varioussolid stating times (FIG. 7). In addition, the initial IV drop, rate ofIV gain, and rate of transesterification were also measured Theseresults are summarized in Table I and shown in FIGS. 6-10. Percent Rateof Percent Percent Percent Ethylene Initial IV Rate of Sample PET PETPhosphite Glycol IV Change Transesterification A 100 0 0 0 0.6400 0.0163— B 67.4 32.6 0 0 0.6145 0.012 0.67 C 67.4 32.6 0 0.125 0.5440 0.0110.86 D 67.4 32.6 0 0.5 0.4478 0.0056 1.78 E 67.4 32.6 0 2 0.3365 -0.00363.56 F 67.4 32.6 1 0 0.6338 0.021 0.25

[0104] As is clear from Table I, if no ethylene glycol is added to thereaction mixture, the rate of transesterification is relatively low.However, by adding an appropriate amount of ethylene glycol to thereaction mixture, the rate of transesterification is increaseddramatically. In particular, by adding 2 weight percent of ethyleneglycol to the reaction mixture, the rate of transesterificationincreases by a factor of more than five relative to a reaction mixtureto which no ethylene glycol was added prior to reaction. Thus, addingethylene glycol to the reaction mixture prior to solid stating allowscontrol of the IV and level of transesterification of the copolymer aswell as the solid-stating time.

[0105]FIG. 6 demonstrates that the intrinsic viscosity of the copolymerdecreases as the amount of ethylene glycol added to the reaction mixtureprior to solid stating is increased. Thus, by adding ethylene glycol,the molecular weight of the copolymer is reduced.

[0106]FIG. 7 shows that the percent transesterification increases as theamount of ethylene glycol added to the reaction mixture prior to solidstating is increased. This is an unexpected result since theconventional wisdom indicates that adding ethylene glycol should reducethe level of transesterification of the copolymer.

[0107]FIG. 8 shows that the initial IV drop in the copolymer increasesas the weight percentage of ethylene glycol added to the reactionmixture prior to solid stating is increased. Hence, the added ethyleneglycol increases the rate at which the molecular weight of the copolymerdecreases.

[0108]FIG. 9 shows that the rate of IV gain during solid stating isreduced as the weight percentage of ethylene glycol added to thereaction mixture prior to solid stating is increased. As a result, theadded ethylene glycol decreases the rate at which the molecular weightincreases.

[0109]FIG. 10 shows that the rate of transesterification increases asthe weight percentage of ethylene glycol added to the reaction mixtureprior to solid stating is increased. The result is surprising since theconventional wisdom dictates that the presence of this additionalethylene glycol should reduce the rate of transesterification of thecopolymer.

[0110] Although several preferred embodiments of this invention havebeen specifically illustrated and described herein, it is to beunderstood that variations may be made to the method of this inventionwithout parting from the spirit and scope of the invention as defined inthe appended claims.

1. A method of copolymerising polyethylene naphthalate (PEN) andpolyethylene terephthalate (PET) comprising: providing PEN having afirst intrinsic viscosity (IV); providing PET having a second IV;reacting the PEN and PET in the presence of alkylene glycol having up to6 carbon atoms to form a copolymerised PEN/PET product having a final IVand a final level of transesterification.
 2. The method of claim 1 ,wherein the copolymerised PEN/PET product comprises about 60 to 95weight percent of PET and about 5 to 40 weight percent of PEN.
 3. Themethod of claim 2 , wherein the copolymerised PEN/PET product comprisesabout 35 to 85 weight percent of PET and about 15 to 35 weight percentof PEN.
 4. The method of claim 1 , wherein the alkylene glycol isselected from the group consisting of propylene glycol and ethyleneglycol.
 5. The method of claim 4 , wherein the alkylene glycol isethylene glycol.
 6. The method of claim 1 , wherein the alkylene glycolis compounded with the PEN and PET prior to forming the copolymerisedPEN/PET product.
 7. The method of claim 1 , wherein the alkylene glycolis added to a reaction chamber in which the PEN and PET arecopolymerised to form the copolymerised product.
 8. The method of claims1, wherein the effective amount of the alkylene glycol is at least about0.05 weight percent based on the total weight of the PEN and PET.
 9. Themethod of claim 1 , wherein the effective amount of the alkylene glycolis about 0.1 to 2 weight percent based on the total weight of the PENand PET.
 10. The method of claim 1 , wherein the effective amount ofalkylene glycol is about 0.1 to 0.5 weight percent based on the totalweight of the PEN and PET.
 11. The method of claim 1 , wherein at leastone of PET and PEN is modified with up 5 to about 15 mol percent of oneor more different dicarboxylic acids containing from 2 to 36 carbonatoms, one or more different glycols containing from 2 to 12 carbonatoms, or a mixture of the one or more different dicarboxylic acids andthe one or more different glycols.
 12. The method of claim 1 , whereinthe reacting step is carried out at a temperature of about 175° C. to250° C. for at least about 6 hours such that a level oftransesterification of the copolymerised PEN/PET product is increased atleast about 5%.
 13. The method of claim 12 , wherein the reacting stepis carried out at a temperature of about 215° C. to 240° C. for about 8to 12 hours such that the level of transesterification of thecopolymerised PEN/PET product is increased about 5 to 25%.
 14. Themethod of claim 1 , wherein the reacting step is carried out at atemperature of about 175° C. to 250° C.
 15. The method of claim 1 ,wherein the second IV is about 0.70 dL/g to 0.75 dL/g.
 16. The method ofclaim 1 , wherein the PET is post-consumer PET (PC-PET).
 17. The methodof claims 1, wherein the amount of the alkylene glycol reduces the rateof IV increase during the reacting step by at least about 10% ascompared to reaction of the PEN and PET in the absence of the alkyleneglycol.
 18. The method of claim 1 , wherein the final IV is greater thanthe second IV.
 19. The method of claim 1 , wherein the amount of thealkylene glycol is no greater than about 2% by total weight of the PENand PET.
 20. The method of claim 1 , wherein a phosphite antioxidant ispresent in the reacting step for reducing the rate oftransesterification during the reacting step.
 21. The method of claim 1, wherein the copolymerised PEN/PET product has a level oftransesterification greater than about 30%.
 22. The method of claim 1 ,wherein both the amount of alkylene glycol and time of the reacting stepare controlled.
 23. The method of claim 1 , wherein the first IV isabout 0.5 dL/g to about 0.8 dL/g, the second IV is about 0.70 dL/g toabout 0.75 dL/g, the final IV is at least 5% greater than the second IV,and the level of transesterification is greater than about 30%.
 24. Themethod of claim 1 , wherein the first IV is about 0.5 dL/g to about 0.8dL/g, the second IV is about 0.70 dL/g to about 0.75 dL/g, the final IVis at least 5% greater than the second IV, and the level oftransesterification of the copolymerized PEN/PET product is increased byabout 5 to 25%.